Cancelling a payment schedule in Adfin only stops new payments being created under it. Any payment that was already raised before you cancelled stays in the queue and will collect on its scheduled date unless you cancel that payment individually.
How to find and cancel an already-raised payment
Open the Schedules view in the sidebar.
Click the schedule.
In the schedule drawer, open the Payment requests tab. You'll see every payment raised under that schedule (each one has its own PR number).
Open the payment and cancel it from there.
If you already know the PR number you can also find the payment directly in the Payments view.
For the full mechanics of how schedules work, see Create a recurring payment schedule.